Membrane cards and needle cards have been successfully used to test integrated chips, wafers, and multichip modules. Needle cards consist of a number of radially arranged resilient needles which exactly correspond to the test points of the IC to be contacted. Since contact with the IC is made by means of these needles, a new card needs to be manufactured for each contact pattern or footprint of the IC pads. Depending on the number of needles, different designs are necessary. If, e.g., 300 needles are used to test a device, it may become necessary to arrange these needles in as many as three levels, since only a limited number of them can be compressed in one ring. Adjusting the needles in a three level formation necessitates a considerable amount of manual work due to an accuracy requirement of the needle tips of about 5 .mu.m. Additionally, the needles are highly sensitive to damage and misadjustment, since they are not mechanically guided over a relatively long distance.
The ever increasing contact density and number of contacts required by more advanced IC generations further limits the use of needle cards. Moreover, it is not always possible to cover the total area of a test card with contact needles, a conclusion which also holds true for membrane cards presently being developed. Although it is possible to create ICs with a very dense arrangement of contact pads, no adequate system exists at present for testing such chips.
Towards the latter part of the 1980s, buckling beam test probe assemblies were introduced. European patent 165331 describes a contact probe arrangement for electrically connecting a test system to the contact pads of a device to be tested, in which wires of highly electrical conductivity and resilient material are used as contact probes. These contact probes are placed onto the contact pads of the device and put under axial stress to achieve low contact resistance, thereby allowing the probes to buckle laterally. This lateral buckling is advantageous since it provides a way to adapt to irregularities in the surface of the device to be tested. The buckling contact probes also adapt to different heights of the contact pads.
U.S. Pat. No. 4,843,315 of common assignee discloses a contact probe arrangement that includes a stack of perforated plates through which extend into a plurality of contact probes. This stack consists of two kinds of plates. The first is provided with circular or square holes permitting a vertical placement of the contact probes onto the contact pads of the device to be tested. The plates of the second kind have oblong, rectangular, square, circular, elliptical or trapezoidal holes. With respect to the second kind, alternating plates are offset with respect to adjacent plates and which, in turn, are aligned with respect to each other. The alignment is such that if axial stress is applied, the contact probe cannot buckle further than the section of the perforation wall limiting maximum buckling. However, neither the needle cards nor the buckling beam contact probe arrangements solve the problem of contacting dense arrangements of contact pads below a 180 .mu.m pitch. Exact positioning of the contact probes is required to allow burn-in simultaneously with conducting pure electrical tests. Furthermore, known assemblies are highly sensitive to misadjustments as well as damage.